This invention relates to a sliding mechanism for a sunroof of an automotive vehicle.
By way of example, the specification of Japanese Patent Application Laid-Open (KOKAI) No. 63-242720 discloses an automotive vehicle having a roof provided with an opening capable of being opened and closed by sliding a sunroof.
As shown in FIGS. 14 and 17, the slide structure of the sunroof described in the abovementioned patent publication includes a support frame b having an upper end portion attached to a sunroof a, a roof rail e having a having a main portion c which is linear and a downwardly curving front end portion d, a guide member f guided and supported by the roof rail e and provided on the lower end portion of the support arm b, and a drive cable g for moving the guide member f back and forth along the guide rail e. The drive cable g is disposed in the channel along the roof rail e. By causing the drive cable g to move the support arm b along the roof rail e, the sunroof a is not only slid back and forth but is also closed or lifted up by the front end portion d of the roof rail e. In FIGS. 14 and 17, the character h represents a driving source for the drive cable g, and i represents weather stripping attached to the edge of the opening in the roof.
In the foregoing construction, however, the part of the drive cable g corresponding to the front end portion d of the roof rail is flexed. As a result, the resistance applied to the drive cable g is large and a driving force cannot be transmitted to the sunroof a sufficiently. This makes it difficult for the sunroof a to be closed and lifted up smoothly.
A known expedient for reducing the resistance of the drive cable is exemplified in FIG. 18. Here a pin j is provided in the tip of the drive cable g so as to project to the side, and the support arm b is provided with a slot k through which the pin j is passed so as to be capable of moving up and down therein. As a result, the support arm b can be moved up and down without flexing the drive cable g.
However, this conventional expedient results in a large frictional resistance between the pin j and the slot k, and therefore it is still difficult to close and lift the sunroof with sufficient smoothness.
In particular, when the sunroof a is brought into pressured contact with the weather stripping i at closing of the opening, the direction of a force applied to the support arm b from the drive cable g and the direction of a force by which the roof rail e attempts to pull down the support arm b are perpendicular to each other, and therefore the frictional force between the slot k and the pin j becomes very large. This makes it difficult to close off the opening with certainty.
A second example of the prior art shown in FIG. 15 is of the type using an inverted T-shaped arm. Specifically, a bracket g' is attached to the sunroof a, the upper end of the support arm b, which has an inverted T-shaped configuration, is pivotally supported on the bracket g', and the guide member i and a rear guide member j', which are movable within the roof rail e, are provided on lower edge of the support arm b. In accordance with this example of the prior art, an amount of lift L can be obtained, which depends upon an amount of arm movement Ht, namely the amount of up-and-down movement of the center Q (the center point between the two guide members i, j') of the lower edge of the support arm b, and an amount of up-and-down displacement of a pivot point P (the point at which the support arm b is pivotally supported on the bracket g') obtained by turning the support arm b up and down about the center point Q.
In the first example of the prior art shown in FIG. 14, however, the amount of lift L of the sunroof a is nothing more than an amount of up-and-down arm movement Hk. Consequently, if the amount of lift L is large, an amount Sk by which the front end d of the roof rail declines also is large. The result is a lower ceiling for the passenger compartment and therefore a passenger compartment with less interior space.
In the second example of the prior art, as shown in FIG. 15, the line segment connecting the pivot point P on the bracket g' and the center point Q becomes vertical when the support arm b is situated on the main portion c of the sun rail e. Consequently, the amount of up-and-down displacement of the pivot point P at the front end portion d is small even when the support arm b is turned up and down motion, and hence this contributes little to an increase in the amount of lift L. In addition, in order to compensate for the increase in the size of the lower portion of the support arm b in the forward and rearward directions owing to the two guide members i, j', the front end portion d of the roof rail e must be extended in length to guide and support the front guide member i. As a result, the downward slope of the front end portion d is enlarged in proportion to the extension in length, and hence there is very little difference between this example of the prior art and the first example described above. Furthermore, though the amount of up-and-down motion of the support arm b can be increased if the front end portion d of the roof rail e is given a large curvature, thereby increasing the amount of displacement mentioned above so that it will contribute more greatly to the amount of lift, the greater curvature leads to more frictional resistance acting upon the guide members i and j'. This makes it difficult to open and close the sunroof a smoothly.